They are the first results from a planned 30-year project to monitor the health of the 2 million residents of Fukushima prefecture.

According to the Japan Times, samples taken from the same 15 people at the beginning and end of May showed that their cumulative individual exposure is approaching the maximum annual "safe" dose of 20 millisieverts.

"It will be difficult for people to continue living in these areas," Nanao Kamada of Hiroshima University, and head of the investigation team, told the newspaper.

Kamada found iodine-131 at doses up to 3.2 millisieverts in
six people in the first round of tests, but none in the second. Half of
any given amount of radioactive iodine decays away every 8 days, so it's
possible most of it had disappeared by the end of May.

Iodine is the main immediate hazard in nuclear fallout, because it accumulates in the thyroid gland, leading to thyroid cancers.

"If they found it in the urine, almost all of it will have been through the thyroid," says Richard Wakeford of the Dalton Institute in Manchester, UK, and an authority on the hazards posed by radioactive material. Almost all cases of thyroid cancer following the Russian nuclear accident at Chernobyl in 1986 were a result of children drinking heavily contaminated milk, he says.

Kamada also found contamination from radioactive caesium in all the Fukushima samples. This brought the doses experienced over about two months to between 4.9 and 14.2 millisieverts.

"The figures did not exceed the maximum of 20 millisieverts a year, but we want residents to use these results to decide whether to move," Kamada told the Japan Times. Isotopes caesium-134 and caesium-137 persist longer in the environment, with half-lives of 2 and 30 years respectively. So while the threat of cancer is less than for iodine, caesium in the soil can potentially contaminate vegetables and other foodstuffs for many years, says Kamada.

Wakeford told New Scientist that the amounts found were hardly surprising given the heavy contamination of areas northwest of Fukushima.

He said that although the radiation was considerably higher than typical annual natural doses of around 1 millisievert, the levels shouldn't pose too much of a hazard provided the amounts begin to fall in coming months.

In the next two weeks, another 110 people from Iitate, Kawamata and nearby Namie will be tested for contamination. In all, 28,000 residents of the three towns will receive initial check-ups, reports NHK. Eventually, 2900 people will be examined by a whole-body counter to measure their internal exposure in more detail.

Meanwhile, the Fukushima prefectural government approved a plan on Friday to issue personal dosimeters to 280,000 children and 20,000 pregnant women in Fukushima. Ten dosimeters will also be installed in each of the 500 elementary schools in the prefecture, reports the Asahi Shimbun.

At Fukushima High School in the City of Fukushima, students have begun their own independent investigation into levels of fallout, reports today's Mainichi Shimbun. They measured radiation at 700 locations in their school in May, and created a radiation map, finding the highest contamination in ditches. At present, they're monitoring contamination in a 14-storey block of flats.

Americans, meanwhile, can expect radioactive caesium from Fukushima to start washing up on the West Coast in five years time, according to the Mainichi Shimbun.

Back at the stricken reactor itself, Tepco operatives yesterday began recycling decontaminated water through reactor units 1, 2 and 3 in a bid to reduce the amount of contaminated cooling water accumulating at the site. At present, an estimated 110,000 tonnes of contaminated water has built up there, with space for storing it rapidly running out.

But according to NHK, Tepco had to halt the operation after 90 minutes because the system developed leaks. By then, it had recycled 1850 tonnes of decontaminated water, treated at a decontamination unit newly installed on 14 June.

4 Comments

I might be being dense (long day so don't be too harsh), but surely if power is not an issue now, then if the contamned water is boiled, there SHOULD be no radioactive elements in the vapour.

The contaminants would stay behind in an ever increasing concentration.

I appreciate evaporating off over 100 million litres of water is not a simple task - but even a 10MW heater should be able to take water at 25C and evaporate at around 14,000 litres per hour. At that rate, in one year all water should have been released through evaporation and a small amount of residual radioactive material remain - along with a vast stockpile of salt if much of this is seawater.

Approx 0.71 KWH of power required to take one litre of water from 25C to vapourisation, the rest is scaling up.

Dave
on June 27, 2011 10:41 PM

"But he expressed surprise that iodine was found, as it should have decayed by a factor of 50 by early May."

Which would mean that either the initial contamination was worse than thought (or acknowledged) -- or that release of radioactive isotopes is ongoing.

@flo; Yes, small risk. What is wrong with that? You think we shouldn't try and evaluate and quantify risk? You think we should just panic blindly at the mention of radiation? ("OMG, I just ate a banana and got a 0.1 uSv radiation dose!")